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Performance evaluation of wave input reduction techniques for modeling inter-annual sandbar dynamics
In process-based numerical models, reducing the amount of input parameters, known as input reduction (IR), is often required to reduce the computational effort of these models and to enable long-term, ensemble predictions. Currently, a comprehensive performance assessment of IR-methods is lacking, which hampers guidance on selecting suitable methods and settings in practice. In this study, we investigated the performance of 10 IR-methods and 36 subvariants for wave climate reduction to model the inter-annual evolution of nearshore bars. The performance of reduced wave climates is evaluated by means of a brute force simulation based on the full climate. Additionally, we tested how the performance is affected by the number of wave conditions, sequencing, and duration of the reduced wave climate. We found that the Sediment Transport Bins method is the most promising method. Furthermore, we found that the resolution in directional space is more important for the performance than the resolution in wave height. The results show that a reduced wave climate with fewer conditions applied on a smaller timescale performs better in terms of morphology than a climate with more conditions applied on a longer timescale. The findings of this study can be applied as initial guidelines for selecting input reduction methods at other locations, in other models, or for other domains.
Evaluating adaptation measures for reducing flood risk : a case study in the city of Colombo, Sri Lanka
Many cities around the world face frequent problems with flooding, which is expected to get worse due to anthropogenic climate change and further urbanization. To tackle these problems often local infrastructural adaptation measures are proposed. In this study a chain of state-of-the-art models is presented that can be used to evaluate the benefits of such measures. Also, a method is presented to calculate the costs of not responding to a changing environment that is slowly aggravating floods. These methods are applied to a case study in the city of Colombo in Sri Lanka. Colombo faces problems with floods that are expected to get worse by further wetland reduction and climate change. Several local measures (infrastructural interventions) are proposed to tackle that problem. This paper shows a method to quantify the expected reduction in future flood damages resulting from the proposed measures, and compares the risk reduction to the proposed measure costs. This is done by creating probabilistic inundation depth maps using a 1D2D hydrodynamic model. A detailed flood damage model and socio-economic development scenarios are then applied to estimate damage with and without the measures. An economic analysis is done to demonstrate the benefits of the measures, which can be used by decision makers. Additionally, calculations are carried out of future flood risk increases when wetland reduction in Colombo continues. In this case, the effect of stopping wetland encroachment is found to be larger than the effect of the structural adaptation measures.
Linking management planning for coastal wetlands to potential future wave attenuation under a range of relative sea-level rise scenarios
Understanding changes in wave attenuation by emergent vegetation as wetlands degrade or accrete over time is crucial for incorporation of wetlands into holistic coastal risk management. Linked SLAMM and XBeach models were used to investigate potential future changes in wave attenuation over a 50-year period in a degrading, subtropical wetland and a prograding, temperate wetland. These contrasting systems also have differing management contexts and were contrasted to demonstrate how the linked models can provide management relevant insights. Morphological development of wetlands for different scenarios of sealevel rise and accretion was simulated with SLAMM and then coupled with different vegetation characteristics to predict the influence on future wave attenuation using XBeach. The geomorphological context, subsidence, and accretion resulted in large predicted reductions in the extent of vegetated land (e.g., wetland) and changes in wave height reduction potential across the wetland. These were exacerbated by increases in sea-level from +0.217 m to +0.386 m over a 50-year period, especially at the lowest accretion rates in the degrading wetland. Mangrove vegetation increased wave attenuation within the degrading, subtropical, saline wetland, while grazing reduced wave attenuation in the temperate, prograding wetland. Coastal management decisions and actions, related to coastal vegetation type and structure, have the potential to change future wave attenuation at a spatial scale relevant to coastal protection planning. Therefore, a coastal management approach that includes disaster risk reduction, biodiversity, and climate change, can be informed by coastal modeling tools, such as those demonstrated here for two contrasting case studies.
Development and test of usability of an operational crop growth system for farmers : TKI Farmers'App (final report)
The goal of this project was to demonstrate the possibility to develop a real-time forecasting system for crop production, enabling water boards, farmers and the insurance broker to improve their services and possibly reduce costs. The setup of both the Aa & Maas and Vechtstromen models within the “Grow with the Flow” operational system shows promising initial results. The value of the system was demonstrated by comparing model results with measurements in the field during the growing season. We successfully finalized the system and demonstrated the possibilities of application for a wet (2016), ‘normal’ (2017), and dry (2018) season.
Veiligheid van damwandconstructies
Dit rapport is het versiag van de laatste fase van het project "Veiligheid van damwandconstructies". In dit rapport worden resultaten gegeven van methoden om het beoogde (optimale) veiligheidsniveau van een constructie te bepalen. Een methode is middels calibratie aan een kiassieke deterministische ontwerpmethode. Resultaten van zon vergelijking ten aanzien van de drie damwandconfiguraties worden in dit rapport gepresenteerd. Aan de hand hiervan is een kiasse-indeling van constructies gemaakt.
Verkenning toekomstig medegebruik windparken
Het doel van deze studie was het verkennen van toekomstig medegebruik in bestaande en geplande windparken. Denkbare typen en categorisering van (innovatieve) technologieën die in 2030 operationeel kunnen zijn werden in kaart gebracht. Via een literatuurstudie en expert judgement is invulling gegeven aan dit doel. De meeste (innovatieve) technologische ontwikkelingen richten zich op het gebruik van het wateroppervlak (drijvend) en de waterkolom (hangend). Het gaat dan om duurzame energie en aquacultuur. Deze vormen van medegebruik kunnen in bijna alle gevallen de doorvaartmogelijkheden in windparken belemmeren. De ruimtelijke voetafdruk (gebruiksruimte) is het grootst voor zeewierkweek (500 km²), schelpdierkweek (mosselen – tientallen km²) en zonne-energie (tientallen km²). De ruimtelijke voetafdruk in termen van onderhoudszone is het grootst van kabels en leidingen (500 tot 750 meter aan weerszijden). Drijvende en statische energie-eilanden en enkele typen van duurzame energie nemen een veiligheidszone van 500 meter in beslag. De kleinste veiligheidszones komt het meest voor bij aquacultuur (ca. 50 meter). Kansen die voortkomen uit de (innovatieve) technische ontwikkeling bestaan uit het gebruik van bestaande elektriciteitsinfrastructuur voor duurzame energie. Drijvende en statische energie-eilanden (incl. schepen) bieden kansen voor opslag en omvorming van energie. Voor aquacultuur is voornamelijk het beschikbare areaal een kans voor opschaling. Voor windparken en andere vormen van medegebruik bestaan de kansen uit het delen van de elektriciteitsinfrastructuur (kostenbesparing), diversifiëring, delen van faciliteiten, bevoorrading, onderhoud & beheer, dataverzameling (metocean) en hulpverleningsdiensten. Risico’s voor duurzame energie zijn storingen in de elektriciteitsinfrastructuur. Het loslaten van materiaal, aanvaringen en beperking van onderhoudsruimte zijn risico’s die voor bijna alle toekomstige vormen van medegebruik van toepassing zullen zijn. Lekkages zijn een risico bij leidingen en drijvende en statische energie-eilanden. Aquacultuur zorgt voor risico’s zoals ziekten, parasieten voor alle typen van aquacultuur. Ontsnappingen, medicijnen, eutrofiering en schadelijke algenbloei zijn risico’s die specifiek met viskweek geassocieerd worden. Risico’s van (innovatieve) technische ontwikkelingen voor de windparken en andere vormen van medegebruik bestaan in bijna alle gevallen uit aanvaringen, beperking van de onderhoudsruimte en het loslaten materiaal.
Accounting for the uncertain effects of hydraulic interactions in optimising embankments heights : proof of principle for the IJssel River
Most alluvial plains in the world are protected by flood defences, for example, embankments, whose primary aim is to reduce the probability of flooding of the protected areas. At the same time, however, the presence of embankments at one area influences hydraulic conditions of downstream areas located on the same river. These hydraulic interactions are often neglected in current flood risk management. The aim of this study is to explicitly acknowledge hydraulic interactions and investigate their impact on establishing optimal embankment heights along a stretch of the IJssel River. We find that the current approach leads to a single solution, while taking into account hydraulic interactions substantially expands the number of promising solutions. Furthermore, under a reference scenario, the current approach is in fact suboptimal with respect to both downstream locations and the system as a whole. Under uncertainty, it performs adequately from a system viewpoint, but poorly for individual locations, mostly due to risk overestimation downstream. Overall, the current approach proves to be too short-sighted, because spatial tradeoffs among locations are neglected and alternative solutions remain hidden. Acknowledging the effect of hydraulic interactions provides policy makers with a broader and more comprehensive spectrum of flood risk management strategies.
Reversed lateral circulation in a sharp estuarine bend with weak stratification
Although the hydrodynamics of river meanders are well-studied, the influence of curvature on flow in estuaries, with alternating tidal flow, varying water levels and salinity gradients, is less well understood. This paper describes a field study on curvature effects in a narrow salt-marsh creek with sharp bends. The key observations, obtained during times of negligible stratification, are 1) distinct differences between secondary flow during ebb and flood, with helical circulation as in rivers during ebb and a reversed circulation during flood, and 2) maximum (ebb and flood) streamwise velocities near the inside of the bend – unlike typical river bend flow. The streamwise velocity structure is explained by the lack of a distinct point bar and the relatively deep cross section in the estuary, which makes that curvature induced inward momentum redistribution is not overcome by outward redistribution by frictional and topographic effects. Through differential advection of the along-estuary salinity gradient, the laterally sheared streamwise velocity generates lateral salinity differences, with the saltiest water near the inside during flood. The resulting lateral baroclinic pressure gradient force enhances the standard helical circulation during ebb but counteracts it during flood. This first leads to a reversed secondary circulation during flood in the outer part of the cross section, which triggers a positive feedback mechanism by bringing slower moving water from the outside inward along the surface. This leads to a reversal of the vertical shear in the streamwise flow, and therefore in the centrifugal force, which further enhances the reversed secondary circulation.
Radium isotope fingerprinting of permafrost : applications to thawing and intra‐permafrost processes
Permafrost in circum‐polar regions has been recently undergoing thawing, with severe environmental consequences, including the release of greenhouse gases and amplification of global warming. Although highly important, direct methods of tracking thawing hardly exist. In a research study conducted at Adventdalen, Svalbard, we identified a permafrost radioisotope fingerprint, and show that it can be used to track thawing. Ratios of long‐ to the shorter‐lived radium isotopes are higher in ground ice than in active layer water, which we attribute to the permafrost closed system and possibly to the long residence time of ground ice in the permafrost. Also, daughter–parent 224Ra/228Ra ratios are lower in permafrost than in the active layer. These fingerprints were also identified in a local stream, confirming the applicability of this tool to tracing thawed permafrost in periglacial watersheds. A combination of radium isotope ratios and 3H allowed the identification of recent intrapermafrost segregation processes. The permafrost radium fingerprint should be applicable to other permafrost areas, which could assist in regional quantification of the extent of permafrost thawing and carbon emissions to the atmosphere.
Disentangling and parameterizing shallow sources of subsidence : application to a reclaimed coastal area, Flevoland, the Netherlands
The natural surface area of many coastal and delta plains has been increased by land reclamation in response to growing populations. These reclaimed lands are often experiencing subsidence. The reclaimed South Flevopolder in the coastal plain of the Netherlands has experienced severe subsidence after its reclamation in 1968. The subsidence is caused by phreatic groundwater level lowering and the associated aeration of the former subaqueous shallow subsurface and increased effective stresses. In this study, surface elevation measurements that quantify the subsidence, conducted annually between 1968 and 1993, and in 2009 and 2012, have been used to constrain and estimate the parameters in models that describe subsidence. For the estimation an Ensemble Smoother with Multiple Data Assimilation was employed. For the forward models, we employed correlations for compression (primary consolidation and creep), oxidation, and shrinkage of coastal deposits. Shrinkage of the aerated clay and organic clay layers was found to be the main contributor to subsidence, and the measurements could be represented well. The quantification of the model parameters allows for better subsidence forecasts. The stochastic method that was employed further facilitates to define a quality measure for forecasts in terms of a covariance matrix or a confidence range.